Pascal (unit)
Pascal (unit) From Wikipedia, the free encyclopedia Jump to: navigation, search This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2011) Pascal Psidial.jpg A pressure gauge reading in psi (red scale) and kPa (black scale) Unit information Unit system SI derived unit Unit of Pressure or stress Symbol Pa  Named after Blaise Pascal In SI base units: 1 Pa = 1 kg/(m·s2) The pascal (symbol: Pa) is the SI derived unit of pressure, internal pressure, stress, Young's modulus and ultimate tensile strength, defined as one newton per square metre.1 It is named after the French polymath Blaise Pascal. Common multiple units of the pascal are the hectopascal (1 hPa ≡ 100 Pa) which is equal to 1 mbar, the kilopascal (1 kPa ≡ 1000 Pa), the megapascal (1 MPa ≡ 1,000,000 Pa), and the gigapascal (1 GPa ≡ 1,000,000,000 Pa). On Earth, standard atmospheric pressure is defined as 101.325 kPa.2 Meteorological reports typically state atmospheric pressure in hectopascals.3 Contents hide 1 Etymology 2 Definition 3 Miscellaneous 4 Uses 4.1 Hectopascal and millibar units 5 See also 6 Notes and references Etymologyedit The unit is named after Blaise Pascal, noted for his experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre (N/m2) by the 14th General Conference on Weights and Measures in 1971.4 Definitionedit The pascal can be expressed using SI derived units, or alternatively solely SI base units, as: {\rm 1~Pa = 1~\frac{N}{m^2} = 1~\frac{kg}{m \cdot s^2}}5 Where N is the newton, m is the metre, kg is the kilogram and s is the second. Miscellaneousedit Standard atmospheric pressure is 101325 Pa (101.325 kPa).6 This definition is used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries. In 1985 the IUPAC recommended that the standard for atmospheric pressure should be harmonized to 101325 Pa.needed The same definition is used in the compressor and the pneumatic tool industries (ISO 2787). The Unicode computer character set has dedicated symbols ㎩ (U+33A9) for Pa and ㎪ (U+33AA) for kPa, but these exist merely for backward-compatibility with some older ideographic character-sets and are therefore deprecated. Usesedit The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit, except in some countries that still use the Imperial measurement system, including the United States. Geophysicists use the gigapascal (GPa) in measuring or calculating tectonic stresses and pressures within the Earth. Medical elastography measures tissue stiffness non-invasively with ultrasound or magnetic resonance imaging, and often displays the Young's modulus or shear modulus of tissue in kilopascals. In materials science and engineering, the pascal measures the stiffness, tensile strength and compressive strength of materials. In engineering use, because the pascal represents a very small quantity, the megapascal (MPa) is the preferred unit for these uses. approximate Young's modulus for common substances 7 Material Young's modulus nylon 6 2–4 GPa hemp fibre 35 GPa aluminium 69 GPa tooth enamel 83 GPa copper 117 GPa structural steel 200 GPa diamond 1220 GPa The pascal is also equivalent to the SI unit of energy density, J/m3. This applies not only to the thermodynamics of pressurized gases, but also to the energy density of electric, magnetic, and gravitational fields. In measurements of sound pressure, or loudness of sound, one pascal is equal to 94 decibels SPL. The quietest sound a human can hear, known as the threshold of hearing, is 0 dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa.8 Hectopascal and millibar unitsedit Main article: Bar (unit) Meteorologists worldwide have for a long time measured atmospheric pressure in bars, where one bar was originally equivalent to the average air pressure on Earth; the bar was divided into a thousand millibars to provide the granularity that meteorologists require. After the introduction of SI units, many preferred to preserve the customary pressure figures. Consequently, the bar was redefined as 100,000 pascals, which is only slightly lower than standard air pressure on Earth. Today many meteorologists prefer hectopascals (hPa) for air pressure, which are equivalent to millibars, while similar pressures are given in kilopascals in practically all other fields, since the hecto prefix is rarely used. Since official metrication, meteorologists in Canada use kilopascals (kPa),910 although in some other countries hectopascals are still in use.11121314151617 As of 17 November 2011 the hectopascal is used in aviation as the altimeter setting. 1 hectopascal (hPa) ≡ 100 Pa ≡ 1 mbar.1 kilopascal (kPa) ≡ 1000 Pa ≡ 10 hPa ≡ 10 mbar. See alsoedit Centimetre of water Metric prefix Orders of magnitude (pressure) Pascal's law Notes and referencesedit 1.Jump up ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), p. 118, ISBN 92-822-2213-6 2.Jump up ^ BIPM Definition of the standard atmosphere "Definition of the standard atmosphere". Retrieved 16 February 2015. 3.Jump up ^ U.S. Federal Meteorological Handbook 4.Jump up ^ bipm.fr 5.Jump up ^ Table 3 (Section 2.2.2), SI Brochure, International Bureau of Weights and Measures 6.Jump up ^ "Resolution 4 of the 10th meeting of the CGPM". Conférence Générale des Poids et Mesures (CGPM). 1954. Retrieved 5 April 2010. 7.Jump up ^ "Tensile Modulus - Modulus of Elasticity or Young's Modulus - for some common Materials". Retrieved 16 February 2015. 8.Jump up ^ "Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits". ResNet. 2010. Retrieved 3 March 2011. 9.Jump up ^ CTV News, weather; current conditions in Montreal 10.Jump up ^ Environment Canada weather, current conditions in Montreal 11.Jump up ^ KNMI 12.Jump up ^ RMI 13.Jump up ^ DWD 14.Jump up ^ JMA 15.Jump up ^ MDD 16.Jump up ^ NOAA 17.Jump up ^ UK Met Office hide v · t · e SI units Base units ampere · candela · kelvin · kilogram · metre · mole · second SI base unit Derived units with special names becquerel · coulomb · degree Celsius · farad · gray · henry · hertz · joule · katal · lumen · lux · newton · ohm · pascal · radian · siemens · sievert · steradian · tesla · volt · watt · weber Other accepted units astronomical unit · dalton · day · decibel · degree Celsius · degree of arc · electronvolt · hectare · hour · litre · minute · minute of arc · neper · second of arc · tonne · atomic units · natural units See also Conversion of units · History of the metric system · Metric prefixes · Proposed redefinitions · Systems of measurement Wikipedia book Book · Category Category · Outline Categories: SI derived units Units of pressure Blaise Pascal